Technical Field
The present invention relates to a battery state estimation apparatus which estimates a state of a secondary battery based on a battery model of the secondary battery.
Related Art
As described in JP-A-2012-159414, this type of apparatus is known which estimates a battery state including a nonlinear domain of current-voltage characteristics of a secondary battery based on a battery model (hereinafter, referred to as a 1RC equivalent circuit model) configured by a DC resistance and an RC equivalent circuit. Specifically, since the time constant is small, electrolyte resistance and both charge-transfer resistance and electric double capacitance are simulated by one DC resistance, and diffusion resistance is expressed by a parallel circuit of a resistor R and a capacitor C.
According to the above conventional art, the 1RC equivalent circuit model does not have a configuration for expressing characteristics of a nonlinear domain. Hence, a filter is set to attenuate a signal of the nonlinear domain and perform calculation by using only data of a linear domain, to react the nonlinear domain. It is known that current-voltage nonlinear characteristics of a secondary battery become dominant as the secondary battery becomes lower in temperature. Specifically, in a domain in which temperature is 0° or less, the nonlinear domain cannot be ignored. Hence, according to the above technique, the amount of data, which can be used for calculation, becomes smaller in a temperature region of 0° or less, which makes the calculation inaccurate. This causes a concern that the accuracy in state estimation of the secondary battery lowers.